1. Field of the Invention
The present invention relates to an optical glass, a hot-molded article and a method of manufacturing the same, and an optical element and a method of manufacturing the same.
2. Description of Related Art
In recent years, high integration and high functionality of equipment that uses an optical system have rapidly progressed with the advent of the digital camera. Under such circumstances, there has been increasingly strong demand for optical systems being made in higher precision, in lighter weight, and more compact. In order to meet this demand, optical designs employing aspherical lenses have been becoming the mainstream.
As a method of manufacturing a lens constituting an optical system, there has been known a method in which glass material is subjected to a cold processing or which a molded glass article obtained by reheat press-molding is subjected to a cold processing. Here, the cold processing refers to machine processings such as grinding and polishing. For optical glass which is subjected to the cold processing, Japanese Unexamined Patent Publication No. 2007-269584, which is expressly incorporated herein by reference in its entirety, discloses boric acid-based optical glass.
Compared to the cold processing mentioned above, there is a method called a hot molding method, where an appropriate amount is taken from an outflowing glass melt and made into a molten glass gob, which is then molded to obtain a preform for an optical element before the molten glass gob gets cooled and solidified. There is also a method called a precision press-molding method, which press-molds a preform to form an optical functional surface of a lens without going through machine processing such as grinding and polishing. These hot molding method and precision press-molding method have been used for stably weight supplying, at low cost, aspheric lenses mainly employing high functional glass. For an optical glass suitable for these molding methods, Japanese Unexamined Patent Publication No. 2002-249337, which is expressly incorporated herein by reference in its entirety, discloses boric acid-rare earth system optical glass showing a high refractive index and low dispersion characteristics.